JP6670840B2 - Imaging optics adapted to the resolution of the human eye - Google Patents

Description

REFERENCE TO RELATED APPLICATIONS This application is a provisional application of U.S. Provisional Application Ser. U.S. Provisional Application No. 62 / 105,905, filed Aug. 21, 2015. Claim priority under 62 / 208,235. Both of these applications are incorporated herein by reference in their entirety.

The present application relates to visual displays, and in particular, to head-mounted display technology.

1. References

WO2015 / 077718 (PCT / US2014 / 067149) on "Immersive small display glasses" referred to as "PCT1"

U.S. Patent Application No. 2010/0277575 A1 by Ismael et al.

U.S. Patent 5,390,047 by Mizukawa.
“Dual-lens by Sensics” http: / /www.roadtovr.com/sensics-ceo-yuval-boger-dual-element-optics-osvr-hdk-vr-headset/ and http: / /sensics.com/sample- quantities-of-osvr-custom-dual-asphere-optics-available-for-purchase /

F. Huang, K. Chen, G. Wetzstein. “The Light Field Stereoscope: Immersive Computer Graphics via Factored Near-Eye Light Field displays with Focus Cues”, ACM SIGGRAPH (Transactions on Graphics 33, 5), 2015. (“Huang 2015 ")

2. Definition

3. Technology level

  Head mounted display (HMD) technology is a rapidly developing field. One aspect of head-mounted display technology provides a fully immersive visual environment (which can be described as virtual reality), where the user is provided by one or more displays while the external environment is visually blocked. Observe only the image. These devices have applications in fields such as entertainment, gaming, military, medical, and industrial.

A head-mounted display is typically one or two displays and their corresponding optics, the optics that project the displays on a virtual screen visualized by the user's eyes, and the external environment. Consists of a helmet that visually blocks and provides support for the components described above. The display may also have a pupil tracker and / or a head tracker, where the image provided by the display changes in response to user movement.

An ideal head-mounted display combines high resolution, wide field of view, light and well-distributed weight, and small size construction. Some techniques have successfully achieved these desired features individually, but at present no technique is known that can combine all of these. This results in an incomplete or more unpleasant experience for the user. Problems can include low levels of realism, eye strain (low resolution or optical imaging quality), failure to create an immersive environment (small field of view), or excessive pressure on the user's head (excessive weight) .

Most current HMDs for immersive virtual reality use one positive lens per eye with a rotationally symmetric plane that projects the light emitted from half of one large 16: 9 digital display into the eye. Used (the other half is used for the other eye). US 2010/0277575 A1 describes one example of such a device. The basic optical function of the HMD is that of a stereoviewer, such as that described in US Pat. No. 5,390,047. Typical dimensions of a 16: 9 digital display are about 4-6 inches (100-150 mm) diagonally, and the display halves used for each eye are rather square with an 8: 9 aspect ratio It is. The optical axis of the rotationally symmetric lens is set perpendicular to the display half and passes approximately through the geometric center of the display half. The focal length at the center of the virtual image (typically located on the lens optical axis) ranges from 35 mm to 45 mm. Lenses typically exhibit slow degradation of image quality for fields that are increasingly far from the on-axis field due to on-axis chromatic and geometric aberrations. For curvature, single lens designs typically exhibit slow pincushion curvature (when analyzed from a digital display to a virtual screen). This curvature also has the effect that the eye pixels around the virtual screen appear to be slightly enlarged in the radial direction rather than square. Curvature conventionally requires pre-processing the image in software to compensate for barrel curvature so that the image on the virtual screen is viewed without curving to show the image on an oppixel of a digital display.

A prior art device called "Dual Lens by Sensics" uses two lenses per monocular instead of one to calibrate axial chromatic and geometric aberrations. The dual lens system still shows pincushion curvature, but only 13% deviation from rectilinear projection for a 90 degree field of view, compared to the single lens design, and a focal length over the center of the 35 mm virtual screen Is claimed to be reduced to This, in turn, requires less deformation of the image when pre-processed, and the eye pixels around the virtual screen appear enlarged by 13% in the radial direction. The embodiments disclosed herein also use two lenses that correct for axial chromatic and geometric aberrations, but in contrast to this prior art, to fit the eye pixel size to the resolution of the human eye in the peripheral field. , Very high pincushion curvature (also very strong deformation required in pre-treatment). This allows our optics to achieve a focal length on the center of the virtual screen that is 1.5 times greater than in "Dual Lens by Sensics" and at the same magnification the center of the virtual screen. The angle size of the upper eye pixel is reduced, and the pixelation of the virtual screen is greatly reduced.

Some embodiments herein project light from a digital display to the eye using an optical system comprised of several lenslet units. PCT1 discloses concepts related to these embodiments as clusters, oppixels, and eyepixels. FIG. 1 (FIG. 3 of PCT1) shows a simple example of only four clusters 104t, 104b, 105t and 105b, which forms the compound image produced by the pixels on the digital display 107. . O-pixels are projected by the microlens array optics to form an image of an eye pixel on a screen 108 (here depicted with a rectangular outline flat for simplicity). Each oppixel belongs to one cluster (the intersection of any two clusters is an empty set, and the set of all clusters is the entire digital display).

Each cluster displays a portion of the image on a virtual screen. Adjacent clusters display portions of the image with some matching shift amount. Some parts of the image appear in more than one cluster. To illustrate this need, a two-dimensional schematic has been added at the top of FIG. It shows the relevant rays to define the edges of the mapping between the O-pixel and the Eye-pixel. In this figure, the virtual screen of the eye pixel is placed at an infinite position, and the directions of the light rays 100a, 101a, 102a and 103a indicate the position of the eye pixel on the virtual screen. The drawing is two-dimensional for brevity, but the actual device that projects the image to the left at the bottom of FIG. 1 is three-dimensional, with four lenslets, two on top and two on the bottom. And not just the two shown at 104 and 105 in the top schematic of FIG. A two-dimensional scheme is used to describe the horizontal coordinates of the mapping between the oppixel and the eyepixel, and similar reasons apply to the vertical coordinates.

The horizontal extent of the virtual screen extends from 100a to 103a. The portion of the image represented in the left cluster 104b is provided by edge rays 100a and 102a arriving at the edge of the pupil region 106 defining vertical lines 100a and 102a on the virtual screen 108. Similarly, portions of the image represented by right clusters 105t and 105b are provided by edge rays 101a and 103a, which define two vertical lines on virtual screen 108. Therefore, the portion of the virtual screen 108 between 101a and 102a is displayed on both the left and right clusters. In particular, a lenslet 104 maps the edge rays 100a and 102a of the virtual screen onto 100b and 102b on the digital display 107. Similarly, lenslet 105 maps edge rays 101a and 103a onto 101b and 103b on digital display 107. The optical design must ensure that the clusters do not overlap, which is achieved with maximum use of the digital display when 101b and 102b coincide. A similar alignment of the upper clusters 104t, 105t with the lower clusters 104b, 105b is evident from FIG.

Due to the partial matching of the information on the cluster, the eye pixel ip1 is formed by the projection of the four oppixels op11, op12, op13 and op14. This set of oppixels is referred to as the "web" of eye pixel ip1. Each web of eye pixels provided at the center of the virtual screen, such as ip1, includes four oppixels. However, a web of eye pixels near the boundaries of the virtual screen may have a small number of oppixels. For example, the web of eye pixel ip2 contains only two oppixels op21 and op22, and the web of ip3 contains only op31.

One aspect of the present disclosure is a display operable to generate a real image; and each lenslet projects a virtual sub-image from a separate partial real image on the display by projecting light from the display to an eye position. Provided is a display device comprising an optical system comprising one or more lenslets arranged to generate. The sub-images combine to form a virtual image that is visible from the eye position. The radial focal length of the optical system decreases with increasing radial angle in the region of the virtual image having a radial angle exceeding 20 ° from the front.

Another aspect is a display operable to generate a real image; and each lenslet generates a virtual sub-image from the individual partial real images on the display by projecting light from the display to an eye position. Provided with an optical system including one or more small lenses provided as described above. The sub-images combine to form a virtual image that is visible from the eye position. The display device is configured to generate a partial virtual image, at least one of which is 1.5 mm fovea by the eye when the eye is at an eye position where the pupil is within the pupil area. And the fovea of the virtual sub-image has a higher resolution than the periphery of the virtual image.

The optical system is configured to generate a virtual sub-image by including a free-form lenslet having a focal length that varies over the effective area of the free-form lenslet.

The radial focal length of the optical system may decrease with increasing radial angle in regions of the virtual image having a radial angle greater than 20 ° from the front.

The radial focal length of the optical system may decrease with increasing radial angle at substantially all points of the virtual image having a radial angle greater than 20 ° from the front.

The sagittal focal length of the optical system may also decrease with increasing radial angle in regions of the virtual image having a radial angle greater than 20 ° from the front.

The sagittal focal length of the optical system may decrease with increasing radial angle at substantially all points of the virtual image having a radial angle greater than 20 ° from the front.

  The optical system includes a fovea formed by light rays incident on a portion of the pupil region of the eye at the eye position at a peripheral angle of less than 2.5 ° in the radial direction of the eye at the point where the individual light is incident on the eye. And the fovea of the sub-image has a higher resolution than the periphery of the sub-image.

The display device is configured to generate a virtual sub-image, wherein at least one of the virtual sub-images is centered on the eye by 1.5 mm when the eye is at an eye position whose pupil is within the pupil range. It has a fovea projected into the fovea, with the fovea of each virtual sub-image having a higher resolution than the periphery of the virtual sub-image.

The display device may include a foveated virtual sub-image projected by the eye into a 1.5 mm fovea of the retina of the eye when the eye is in an eye position where its pupil is within the pupil area, with at least one lenslet. And generating a peripheral virtual sub-image from at least one other lenslet that is projected by the eye onto a portion of the retina outside the fovea, wherein the foveal virtual image comprises: It has a higher resolution than the peripheral virtual image.

The display device is configured to generate a partial virtual sub-image, wherein at least one of the partial virtual sub-images is at least 1.5 mm from the eye when the eye is at an eye position where the pupil is within the pupil range. And the portion of each virtual sub-image has a higher resolution than the periphery of the virtual sub-image.

The at least one lenslet produces a foveated partial virtual image projected by the eye into a 1.5 mm fovea of the retina of the eye when the eye is at an eye position whose pupil is within the pupil area. A foveal lenslet configured to produce a peripheral virtual lens image projected by the eye onto a portion of the retina outside the fovea, wherein the foveal virtual image is Have a higher resolution than the peripheral virtual image.

An optical system having a first optical element having an optically distinguishable first ring of a first sub-element and a second optical element having optically distinguishable second and third rings of a second and third sub-element; An optical element may be provided. The alternating sub-elements in the first ring form separate lenslets with the continuous sub-elements in the second ring, and the remaining sub-elements of the first ring form the continuous sub-elements and separate lenslets in the third ring Can be formed.

The first and second optical elements may be opposite surfaces of the thick lens.

Also provided is headgear comprising a display device according to any of the above aspects, comprising a mount for positioning the display device on a human head such that the eye position of the display device matches the human eye.

The headgear may further comprise a second display device implemented such that the eye position of the second display device matches the second eye of the person.

The first display device and the second display device of the headgear may be substantially the same. For example, they are substantially identical or are mirror images of one another.

The displays of the first and second display devices may be part of a single physical display.

The above and other aspects, features and benefits will become apparent from the following more particular description of certain embodiments, presented in conjunction with the following drawings.

FIG. 1 is a schematic diagram of the mapping from eye pixels to oppixels (prior art).

FIG. 2 shows the typical human eye angular resolution as a function of peripheral angle.

FIG. 3 is a mapping function of three different embodiments. Linear, rectilinear, and adaptive maps are shown.

FIG. 4 shows radial focal length distributions for the same three embodiments as FIG.

FIG. 5 is an isometric view of a two-lens design providing the adaptive mapping and radial focal length values given in FIGS.

FIG. 6A is a two-dimensional cross section of the two-lens adaptation design shown in FIG. Back rays of different eye pixels are plotted and travel toward the display from the creative pupil displaced from the center of the eye.

FIG. 6B shows the same two-dimensional cross section, but the rays corresponding to those acquired by the pupil when the eye gazes forward.

FIG. 7A is a schematic isometric view of an embodiment in which the eye and two optics performing a squeezed mapping from oppixels to eyepixels can be seen.

FIG. 7B is a schematic front view of the two optical devices from FIG. 7A.

FIG. 8 is a cross section of one possible embodiment from FIGS. 7A and 7B.

FIG. 9 is a mapping function of a linear mapping compared to a rotation and freeform fit embodiment.

Human visual resolution is highest in the part of the scene that is imaged in the fovea (of the order of 1.5 mm in diameter) and decreases rapidly as one moves away from that part. FIG. 2 shows the typical human eye angular resolution (angle) as a function of peripheral angle (according to JJ Kerr, “Visual resolution in the periphery”, Perception & Psychophysics, Vol. 9 (3), 1971). (Angular resolution). If a spherical coordinate system with poles on the gaze vector is considered (thus, the peripheral angle corresponds to the polar angle), the angular resolution does not depend on azimuth (azimuth). Furthermore, the human visual resolution is approximately isotropic, meaning that the ability to distinguish between two point sources does not depend on the orientation of the line connecting the two points.

Because the resolution of the human eye is much coarser in the peripheral field of vision than near the gaze direction, we apply the design conditions (focal length and image quality across the virtual screen) of any of the embodiments herein to the optics. It can be adapted and the eye pixels of the virtual screen are less precise than exactly required (because the eyes do not enjoy it).

By employing a focal length across the virtual screen that fixes the magnification from oppixel to eye pixel, we reduce the size of the eye pixel in the gaze area of the virtual screen and increase it in the outer area of the virtual screen. . This makes the eye pixels in the gaze area of the virtual screen smaller (because the total number of oppixels is equal) than in a fixed pixel size system, and therefore the resolution of that area of the virtual image without effectively degrading the rest Improve. This is because the human brain does not sense the reduced resolution in the surrounding area. Because human resolution is isotropic, the control of eye pixel size must be done in two dimensions for optimal design.

To match the image quality across the virtual screen, we can achieve a configuration where the eye pixels are approximately equally resolved by the optics. For any given eye pixel, the desired image quality depends on the position of the pupil within the pupil range and adaptation for the worst case for a pupil position whose peripheral angle for that eye pixel is at its minimum. Note that this must be done. With respect to the Modulation Transfer Function (MTF), this fit means that the MTF value at the Nyquist frequency of the eye pixel for its worst pupil position should ideally be approximately equal across the virtual screen. I do. Alternatively, with respect to the geometric size of the spot, the ratio of the angular rms diameter of the spot on the virtual screen to the size of the eye pixel for the worst pupil position is ideally reduced to the virtual screen. Should be approximately equal over time. If the optical system is ray-traced in the opposite direction (from the eye to the point of the virtual screen and reaches the display), this adaptation of the optical quality will result in the worst pupil (although the focal length will change). This means that the ratio of the rms diameter of the spot on the digital display to the size of the sub-pixel for the position should ideally be approximately equal across the display.

PCT1 (see paragraph 0309 on page 65) introduced the idea of an optical design in which the image quality was adapted to that of human vision, but the adaptation of the focal length was one dimension, It was limited to the extreme peripheral angles only. Here, we do not only match the image quality, but further develop the adaptation to match the adaptation focal length for the entire outer area of the virtual screen in one and two dimensions. .

Section 5 describes an embodiment of a rotationally symmetric optical system that only controls the size of the eye pixel in the radial direction, and Section 6 describes a free-form surface (ie, rotationally symmetric) that controls the size of the eye pixel in two dimensions. An embodiment having an optical system (having no optical power) will be described.

4. Mapping function and focal length

を、各々、仮想スクリーンの球座標の極及び方位角（azimuthal angles）とする。

の方向が水平ラインを規定し、θ＝０が前方向と呼ばれる。関数

が写像関数と呼ばれる。逆写像関数が、

により与えられる。 To further clarify the description of the embodiments disclosed herein, formal definitions of mapping functions and focal lengths will now be described. Let (ρ, φ) be the polar coordinates of point r on the digital display,

Are the polar and azimuthal angles of the spherical coordinates of the virtual screen, respectively.

Defines the horizontal line, and θ = 0 is called the forward direction. function

Is called a mapping function. The inverse mapping function is

Given by

のラジアル焦点距離（radial focal length）f_radが

と記載される。サジタル焦点距離が

である。ラジアル又はサジタルとは異なる他の方向について、焦点距離が、

により与えられ、ここで、αは、ラジアル方向と焦点距離が計算される方向により形成される角度である。焦点距離は、特定の方向における写像の膨張（expansion）又は収縮（shrinking）を意味する。物体とイメージの間の写像が等角（conformal）である時、

がαから独立し、これは、写像の膨張又は収縮が等方性（isotropic）であると言うに等しい。対応のオピクセルが仮想イメージ上で光学系を通じて見られる時の方向α沿いのアイピクセルの角度範囲は、焦点距離上の物理的なオピクセルの直径であり、すなわち、

である。従って、方向αにおけるアイピクセルのサイズは、焦点距離

に逆比例する（簡潔さのため、円形のオピクセルが本明細書で検討されるが、この理由は、通常の正方形のオピクセルに簡単に拡張可能である）。ヒトの目の解像度が、周辺角度（peripheral angle）に依存するが、より良好な近似において（in good approximation）等方性であり、解像度が評価される方向αに依存しない。アイピクセルの角度範囲がαとは無関係であることが望ましい（さもなければ、解像度が、最大角直径（the greatest angular diameter）により与えられる）。オピクセルの直径が、一般的に、非常にαと一定であり、従って、αとは独立した

が、一般的に望まれる。 Virtual screen direction

The radial focal length f _rad of

It is described. Sagittal focal length

It is. For other directions different from radial or sagittal, the focal length is

Where α is the angle formed by the radial direction and the direction in which the focal length is calculated. Focal length refers to the expansion or shrinking of a map in a particular direction. When the mapping between the object and the image is conformal,

Is independent of α, which is equivalent to saying that the expansion or contraction of the map is isotropic. The angular extent of the eye pixel along direction α when the corresponding oppixel is viewed through the optical system on the virtual image is the diameter of the physical oppixel at the focal length, i.e.,

It is. Thus, the size of the eye pixel in direction α is the focal length

(For simplicity, circular oppixels are considered herein, but the reason is easily scalable to regular square oppixels). The resolution of the human eye depends on the peripheral angle but is isotropic in better approximation and does not depend on the direction α in which the resolution is evaluated. It is desirable that the angular range of the eye pixel be independent of α (otherwise the resolution is given by the greatest angular diameter). The diameter of the oppixel is generally very constant at α and therefore independent of α

Is generally desired.

である。ラジアル焦点距離は、

であり、サジタル焦点距離は、

である。 Now, suppose we have a rotationally symmetric optical imaging system, where the axis of symmetry is the direction θ = 0, and this direction is projected on the digital display at the point ρ = 0. Due to rotational symmetry, the mapping function is that only ρ depends on θ, ie,

It is. The radial focal length is

And the sagittal focal length is

It is.

に一致し、θの増加関数である。周辺においてより大きいアイピクセルに代えて直線系（rectilinear）写像が用いられるならば、視野の周辺に向けてアイピクセルを次第に小さくする。仮想スクリーンの注視領域（θ＝２０°）のエッジで、アイピクセルは、θ＝０よりも６％だけ小さく、１００°の視野（θ＝５０°）のエッジで、θ＝０よりも３５％だけ小さい。先に述べたように、実際に目がこれらのエッジピクセルを注視しないため、これは有用ではない。 The mapping of the standard optics of the imaging optics is a rectilinear projection, ρ (θ) = ftan θ, where f is θ = 0 (center of the virtual screen) and only f _rad = It is a constant equal to f _sag . Radial and sagittal focal length

And is an increasing function of θ. If a rectilinear mapping is used instead of larger eye pixels at the periphery, the eye pixels are progressively smaller toward the periphery of the field of view. At the edge of the gaze area (θ = 20 °) of the virtual screen, the eye pixel is 6% smaller than θ = 0, and at the edge of the 100 ° field of view (θ = 50 °), 35% than θ = 0. Only small. This is not useful because, as mentioned earlier, the eye does not actually gaze at these edge pixels.

この写像において、アイピクセルが、直線系（rectilinear）写像よりも小さく増大するが、θ＝４５°で、θ＝０のアイピクセルのラジアル方向に等しく、θ＝０のアイピクセルよりもサジタル方向において１１％小さい。従って、まだ、光学系は、我々の視覚が増加を検知することなくθ＞２０°からアイピクセルが漸増できる事実を上手く利用していない。 The HMD of a single lens usually deviates from a rectilinear mapping, presents some pincushion curvature, and a linear mapping ρ (θ) = fθ (where again, where f = 0, virtual At the center of the screen, which is a constant equal to f _rad = _fsag ). For this mapping function, the total θ and the increasing function

In this mapping, the eye pixel grows smaller than the rectilinear mapping, but at θ = 45 °, which is equal to the radial direction of the eye pixel at θ = 0 and more sagittal than the eye pixel at θ = 0. 11% smaller. Thus, the optics have yet to take advantage of the fact that our vision can gradually increase the eye pixels from θ> 20 ° without detecting the increase.

6. Embodiment of rotationally symmetric optical system

Here we present a rotationally symmetric optical system in which the radial focal length f _rad is a decreasing function that slopes approximately constant as a function of θ outside the gaze area of the virtual screen, where the eye pixel at least Significantly increased in the direction, indicating that the focal length is better adapted to the resolution of the human eye. Furthermore, the image quality in the optical system is also generally adapted to the eye resolution.

FIG. 3 shows a graph of the mapping function ρ = ρ (θ) of the selected adapted embodiment 301, along with the mapping functions of the rectilinear mapping 302 and the linear mapping 303. All of these are designed to work with the same 100 ° field of view and the same 5.7 ″, 145 mm diameter, 16: 9 aspect ratio digital display. One half of the display is for each eye. And the distance from the center of the display (where the optical axis of the lens passes) to a point near the edge is about 32 mm.

The three curves in FIG. 3 pass through the origin (θ = 0, ρ = 0) corresponding to the center of the virtual screen (on-axis field of the optical system), and pass through the point (θ _end = 50 °, ρ _end = 32 mm). Terminate with The rectilinear mapping 302 is lower than the linear mapping 303 for all angles, but the curve 301 of the adapted design is above the linear mapping 303. As a result, curve 301 starts at the origin with a derivative higher than the ratio ρ _end / θ _end , as opposed to what occurs in linear mapping curve 303, but has a derivative that is smaller than the ratio ρ _end / θ _end. The function ends at points ρ _end and θ _end . Because these derivatives are simply radial focal lengths (when the abscissas are expressed in units of radians), this is achieved by reducing the radial focal length around the periphery (ie, A radially larger eye pixel (301) means having a larger focal length (ie, a smaller eye pixel) at the center of the virtual screen than 302 and 303.

FIG. 4 shows a graph with radial focal lengths corresponding to the four mappings: 401 corresponds to the adapted embodiment, and 402 and 403 correspond to rectilinear and linear mapping, respectively. Since the curves 301, 302 and 303 in FIG. 3 share the same endpoint and the curve in FIG. 4 is a derivative of the curve in FIG. 3, either the horizontal axis or the line at θ = 0 and θ = 50 ° The areas closed by the curves 401, 402 and 403 are the same.

By way of comparison, Tables 1 and 2 assume a 2560 × 1440 Opixel display (Opixel pitch = 50 microns) and show the center and edge values of the virtual screen for several parameters, respectively. The parameters selected are focal length, eye pixel angle size, eye pixel density (number of eye pixels per angle), and Nyquist frequency on the virtual screen (the angular frequency of the on-off frequency of the eye pixels). .

According to Table 1, at the center of the virtual screen (θ = 0), the eye pixel size of the adapted embodiment is 3 minutes (arcmin), about 1.5 times smaller than the linear case, rectilinear) by more than twice. Unfortunately, in a 2560 × 1440 operapixel digital display, a 3 minute (arcmin) eye pixel is required (because the human eye resolves 2 minute (arcmin) as suggested in FIG. 2). Although still distinguishable, they are identified to a lesser extent than the other two mappings.

According to Table 2, at the edge of the virtual screen (θ _end = 50 °), the radial size of the eye pixel in the adapted embodiment is 28 minutes (arcmin), about 6 times larger than the linear case, (Rectilinear) 7 times larger. Although 28 minutes (arcmin) appears to be a high value, when the eye gazes forward and the peripheral angle is 50 °, the resolution limit of the human visual field is 50 minutes (arcmin) (see FIG. 2). No roughening is observed. However, the selected design condition is not when the eye looks forward, but when the eye rotates to θ = 20 ° and to the edge of the normal viewing area of the virtual screen. Next, the peripheral angle is 50-20 = 30 °, and according to FIG. 2, the resolution of human vision is 30 minutes (arcmin), which is close to 28 minutes (arcmin) in the adapted embodiment.

（図４では不図示）は、この回転対称設計においてラジアル焦点距離ほど低減されない。特には、仮想スクリーンのエッジf_sag=ρ_end/cosθ_end=４１ｍｍで、周辺領域におけるアイピクセルが、この適合設計においてラジアル方向に大きく長尺にされる。セクション７で開示のように、両方の焦点距離がより近い値を取ることができるため、回転対称性を打破することだけが、適合された解像度の全利益を享受できる。 Sagittal focal length

(Not shown in FIG. 4) is not reduced as much as the radial focal length in this rotationally symmetric design. In particular, at the edge f _sag = ρ _end / cos θ _end = 41 mm of the virtual screen, the eye pixels in the peripheral area are largely elongated in the radial direction in this adaptive design. Since both focal lengths can take closer values, as disclosed in Section 7, only breaking the rotational symmetry can enjoy the full benefit of the adapted resolution.

Assuming that the number of aspheric surfaces is sufficient (preferably four or more), the adaptive mapping curve 301 can be realized by an optical system using a plurality of rotationally symmetric optical surfaces. As the number of surfaces increases, the degrees of freedom increase and the fit is better achieved, while the design of fewer surfaces has more limited optical properties, and therefore, less sharp tilt of the mapping 301 .

Although the specification is not limited to a particular optical configuration, a particular example of a two lens will now be disclosed. FIG. 5 shows a perspective view of a two-lens design providing the adaptive mapping and the radial focal length values given in FIGS. A separate lens pair consisting of refractive lenses 503 and 504 is located between each eye 501 and the display 502. Each half of the display (divided by the center line 505) works with one eye. Due to the particular dimensions (5.7 ", 145 mm, diagonal) of the 16: 9 display used in this design, the center of each eye for the average standard interpupillary distance is centered on a separate half of the display 506. Aligned.

FIG. 6A is a two-dimensional cross section of a two-lens fit design, showing the profile of the eye 601, the display 602, and both lenses 603 and 604. Back rays for different eye pixels are plotted, starting from the conceptual pupil 605 (which is displaced from the center of the eye for simplicity of geometry) to the display and impinging on different oppixels for different eye pixels. This pupil 605 allows one to simulate the properties of the eye pixels as they are gazed while the eyes are rotated, and these gazed eye pixels are therefore the eye pixels whose properties should be the highest . The ray tracing simulation result for the case of FIG. 6A shows that when the eye gazes at the eye pixel, the other wavelength rms spot diameter of the back ray incident on the display is in the range of the normal gaze area of the virtual screen, θ = 0 to θ. = 20 ° range for 20 ° (ie, less than the 50 micron pixel pitch in the previous example).

FIG. 6B is the same two-dimensional cross section, but the rays shown correspond to those acquired by the pupil when the eye gazes forward. As the peripheral angle increases, the image quality of these rays can be progressively relaxed, as allowed by the reduced resolution of the human eye.

As can be seen from FIGS. 6A and 6B, the actual pupil (having a typical diameter of only about 3 mm in good illumination) is at the point where the ray meets the ray sphere. Only at certain times does any ray enter the eye. If the ray is approximately radial to the eyeball 601 at the point where the ray enters the eye, the ray will reach the fovea. If the ray obliques to the eyeball at the point where the ray enters the eyeball, the impact ray reaches the surrounding retina. Since the gaze direction is approximately the radius passing through the center of the pupil, an angle of incidence of about 2.5 degrees, corresponding to a peripheral angle of about 2.5 degrees, can be understood as the limit of fovea rays. . See the light rays incident on “virtual pupil” 605 in FIG. 6A. If the gaze changes, the pupil moves and a different beam reaching the new pupil position is incident on the eye, and the same considerations are applicable for different beams. Thus, by ensuring that the image quality of the optics of the lenses 603, 604 is maximal for near radial rays, it is not necessary to track the gaze direction movement and to achieve the optics or real image Without actively adapting to the display 602, it is ensured that the highest image definition is always projected into the fovea.

As shown in FIGS. 6A and 6B, different light rays from the same oppixel pass through different points of the lenses 603, 604 and reach different parts of the pupil range of the eye 601. The angle of incidence at which each ray enters the eyeball 601 depends more closely on the point at which the ray enters the eyeball 601, and is more closely related to the point at which the ray enters the optical surfaces of the lenses 603, 604. With proper design of the lenses 603, 604, the image quality for each ray is therefore highly correlated to the angle of incidence at which the ray is incident on the eye, so that the fovea rays are sharply focused. Can be singled out. In particular, as best seen in FIG. 6B, most of the marginal rays pass through the outer portion of lens 603, which can therefore be shaped with the lowest image quality.

ここで、a₀は、（ディスプレイから測定される）光軸に沿う頂点位置（vertex position）であり、kは、円錐定数、δ=１/R、R頂点での半径、g_2i+4は、フォーブスＱ−ｃｏｎ多項式Q_i ^conの係数である（Forbes, Shape specification for axially symmetric optical surfaces, Optics Express, Vol. 15, Issue 8, pp. 5218-5226 (2007)）。例えば、図６Ａのレンズに対するこのフィッティングパラメータの具体的な値について、k次元とｍｍ^-1におけるδを除く全てが、ｍｍにおいて、次の表３に示されており、ここで、表面は、ディスプレイから目への光線の伝播におけるそこへの入射順においてＳ１〜Ｓ４として順序付けられる。目が前方向を注視しているときのディスプレイから瞳までの距離は６４．９４ｍｍである。座標のｚ軸は、目からディスプレイに向いており、原点は、ｚ軸とディスプレイの交点にある。レンズ材料は、レンズ６０４ではポリメチルメタクリレート（ＰＭＭＡ）、レンズ６０３ではポリスチレン（ＰＳ）である。

The profile of the axisymmetric aspheric surface of the lens is well fitted by the following standard formula:

Where a ₀ is the vertex position along the optical axis (measured from the display), k is the conic constant, δ = 1 / R, radius at the R vertex, g _{2i + 4} is a coefficient of Forbes Q-con polynomial ^{_{Q i con (Forbes, Shape specification}} for axially symmetric optical surfaces, Optics Express, Vol. 15, Issue 8, pp. 5218-5226 (2007)). For example, for specific values of this fitting parameter for the lens of FIG. 6A, all but k-dimensions and δ in mm ⁻¹ are shown in Table 3 below in mm, where the surface is the display Are ordered as S1 to S4 in the order of incidence there upon in the propagation of light rays from to the eye. The distance from the display to the pupil when the eye gazes forward is 64.94 mm. The z-axis of the coordinates points from the eye to the display, and the origin is at the intersection of the z-axis and the display. The lens material is polymethyl methacrylate (PMMA) for the lens 604, and polystyrene (PS) for the lens 603.

7. Embodiment of free-form surface optical system

In earlier embodiments of the rotating optics, the adaptation of the eye pixel magnification is limited to the radial dimension. In this section, we disclose a free-form optic that can control the size of the eye pixel in two dimensions.

To solve this problem, we have developed a new approach based on etendue squeezing applied to non-imaging designs and more widely described in US Patent No. 8,419,232 to Juan C. Minano et al. An embodiment is proposed. FIG. 7A is a perspective view of an embodiment in which an eyeball 701 and optical devices 702 and 703, which can be generally a lens surface, a double-sided lens, or any other optical device, are seen. The display is not plotted for clarity of the drawing, but sectors such as those identified at 703 are also identified as clusters. Optical devices 702 and 703 present central regions 714 and 715 that work together, while the remaining regions of both devices are divided into sectors. The sectors belonging to 703 are distributed along the outer ring, while the sectors 702 are distributed along two different outer rings. The sagittal angular range of the 702 sector is half the sagittal angular range of the 703 sector. On the other hand, the angular range of the tangential direction of the sector 702 is twice the angular range of the tangential direction of the sector 703. In this way, sectors are conveniently tessellated, as are clusters on digital displays.

FIG. 7B shows a front view of both optical devices 702 and 703, which are highlighted to illustrate how the five sectors are arranged to operate in pairs. In this way, sectors 704, 705, 706, 707 and 708 of device 702 cooperate with sectors 709, 710, 711, 712 and 713 of device 703, respectively. Sectors 704-708 must be tessellated to ensure that no significant gaps are visible from the eye, while microlenses 709-713 can indicate gaps (thus, FIG. 7B). The areas shown as 709-713 are only the largest areas that a sector can occupy.)

FIG. 8 shows a cross-section of a possible implementation of the embodiment of FIG. 7A where each of the optical devices 702 and 703 is a separate free-form surface of a thick lens. Thus, sectors 704, 705, 706, 707 and 708 of surface 702 cooperate with sectors 709, 710, 711, 712 and 713 of surface 703, respectively, to form lenslets (704-709, 705-710, etc.). To form FIG. 8 shows a display 801, an eye 802, and three lenslets of this thick lens (all other peripheral lenslets can be superimposed on one of the three lenslets of the presentation by rotation). .

The first central lenslet is rotationally symmetric about the central axis 813, and its cross-sectional profiles 811 and 812 correspond to the central regions 714 and 715 of FIGS. 7A and 7B. The second lenslet is a free-form lenslet that is symmetric with respect to the plane and corresponds to sectors 705 and 710 in FIGS. 7A and 7B. Lines 809 and 808 in FIG. 8 are cross-sectional profiles in the plane of symmetry including axis 813 in FIG. 8 and line 717 in FIG. 7B. The third lenslet is also free-form, symmetric about another plane, and corresponds to sectors 708 and 713 in FIGS. 7A and 7B. Lines 806 and 807 in FIG. 8 are the cross-sectional profiles in the plane of symmetry including axis 813 in FIG. 8 and line 716 in FIG. 7B. Note that the profiles of the second and third lenses are not coplanar and are drawn together in FIG. 8 for this description only. In addition, the ray trajectory is reversed, and the rays in this description propagate from the eye to the digital display.

  The back ray 810 passes through the central portions 812 and 811 of the lens from the eye and enters the central portion of the display 801. On the other hand, reversed fans of rays 803 and 804 pass through the peripheral areas 806-807 and 808-809 of the lens and enter the external area of the display 805. Ray 804 (plotted in dashed line) is incident on dashed surface 808 and then on dashed surface 809 and is directed to the display. On the other hand, ray 803 (plotted as a solid line) is incident on surface 806 and then incident on surface 807 and is directed to the display. Note that the pair of surfaces 808-809 collect backlight with a smaller peripheral angle than the pair of surfaces 806-807.

The tessellation of clusters and lenslets described herein reduces sagittal focal length as compared to a rotating solution, leaving room for achieving a larger radial focal length at the center of the virtual screen. FIG. 9 illustrates this and shows a schematic curve of the mapping function 901 of this free-form embodiment along a plane of symmetry. The cross section θ = 0-25 ° corresponds to the rotationally symmetric small lenses 714, 715. The portion of the curve 901 at θ = 25 ° -37.5 ° corresponds to the ray-fan 804 shown in FIG. 8 and reaches the edge of the digital display (16: 9, 5.7 ″). The last part of the curve 901 at θ = 37.5 ° -50 ° corresponds to the ray 803 shown in FIG. 8 (actually on the same plane as 804 as described above). No) and also reaches the edge of the digital display. For comparison, the curve corresponding to the linear mapping function 902 and the rotationally symmetric mapping function 903 of section 6 are also shown.The squeezed mapping technique described above By increasing the size of the eye pixel in the sagittal direction through, a large focal length (larger tilt) is obtained at the center of the virtual screen (70.5 mm in the selected example). Allow the same tilt to be maintained in the angular range, as in a rotationally adaptive design, in the angular range θ = 25 ° -50 °, and therefore have the same radial focal length (and hence the same radial focal point). length).

As can be seen from FIG. 9, the curve 901 may be discontinuous at the boundaries between lenslets, but if the discontinuity is well designed, the slope of the curve may be continuous even if the curve itself is not. is there. The step corresponding to the boundary between rays 804 and 803 is shown in dashed lines in FIG. 9 to emphasize that, at least in the ideal case, it is discontinuous and not a segment of negative slope. Any deviations from the idea, such as rounding the cusp between lenslets, to represent places where light rays can scatter in unwanted directions and degrade image quality can be kept to a minimum. preferable.

Although a particular embodiment has been described, the preceding description of the currently contemplated modes of implementing the invention is not to be taken in a limiting sense, but is merely made for the purpose of describing certain general principles of the invention. Variations from the particular embodiment described are possible. For example, the above-referenced patents and applications, which have been cross-referenced, describe systems and methods that may be advantageously combined with the teachings of the present application. Although particular embodiments have been described, those of skill in the art will understand how to combine the features of the different embodiments.

The full scope of the invention is determined by reference to the claims, and features of any two or more claims may be combined.

Claims (21)

Display is operable to generate a real image; by and each lenslet to project light to the eye position from the display, arranged to generate a virtual sub-image from the individual partial real image on the display An optical system comprising one or more lenslets,
The virtual sub-images combine to form a virtual image that is visible from the eye position;
The display device, wherein both the radial and sagittal focal lengths of the optical system decrease with increasing radial angle in a region of the virtual image having a radial angle greater than 20 degrees from the front. The radial focal length of the optical system, before decreases according to substantially increase the radial angle at all points of the virtual image having a radial angle of more than 20 ° from the direction, the display device according to claim 1. The sagittal focal length of the optical system, before decreases according to substantially increase the radial angle at all points of the virtual image having a radial angle of more than 20 ° from the direction, the display device according to claim 1. When the eye is the pupil in the eye position within the pupil range, the at least one virtual sub-image has a central fossae projected on the fovea (fovea) of 1.5mm of the eye by the eye, the Configured to generate a virtual sub-image,
Central fossae of each said virtual sub-image has a higher resolution than the peripheral portion of the virtual sub-image display apparatus according to claim 1.   Generating, from the at least one lenslet, a foveal virtual subimage projected by the eye into a 1.5 mm fovea of the retina of the eye when the eye is at an eye position whose pupil is within the pupil area; Also configured to generate, from at least one other lenslet, a peripheral virtual sub-image projected by the eye on a portion of the retina outside the fovea, wherein the foveal virtual image is The display device according to claim 1, wherein the display device has a higher resolution. A first optical element having an optically distinguishable first ring of a first sub-element and a second optical element having optically distinguishable second and third rings of a second and third sub-element; comprising a second optical element, the first sub-element of the first set in the first ring, the second to form a sub-element and separate lenslet adjacent in the second ring, the first sub second set of the first ring element, a third sub-element and a separate small lens adjacent in the third ring, a display device according to claim 1. The display apparatus according to claim 6 , wherein the first and second optical elements are opposite surfaces of a thick lens. A headgear comprising the display device according to claim 1, comprising a mount for positioning the display device on a human head such that an eye position of the display device coincides with a human eye. 9. The headgear of claim 8 , comprising a second display device implemented such that an eye position of the second display device matches a second eye of a human. The display device and the second display device are substantially identical, headgear according to claim 9. The display of the display and the second display device of the display device is part of a single display, headgear according to claim 9. Display is operable to generate a real image; by and each lenslet to project light to the eye position from the display, arranged to generate a virtual sub-image from the individual partial real image on the display An optical system comprising one or more lenslets,
The virtual sub-images combine to form a virtual image that is visible from the eye position;
Wherein the optical system, when the eye is the pupil in the eye position within the pupil range, the at least one virtual sub-images, the fovea, which is projected to the eyes of 1.5mm fovea of the eye (fovea) having parts, said configured to generate a virtual sub-image, the central fossae of the virtual sub-images, have a resolution higher than the peripheral portion of the virtual image,
The display device, wherein a sagittal focal length of the optical system decreases with an increase in a radial angle in a region of the virtual image having a radial angle exceeding 20 ° from a forward direction . The optical system is formed by light rays entering any part of the pupil range of the eye at the eye position at a peripheral angle of less than 2.5 ° in the radial direction of the eye at the point where the individual light is incident on the eye. is configured to generate the virtual sub-image having a center epigastric that, the central fossae of the virtual sub-image has a higher resolution than the peripheral portion of the virtual sub-image, digital according to claim 12 Display device. The optical system is configured to generate the virtual sub-image by providing a compact lens of a free curved surface having a focal length that varies across the effective area of the free-form surface lenslets, digital claim 12 -Display device. The radial focal length of the optical system is reduced with the increase of the radial angle in the region of the virtual image having a radial angle of more than 20 ° from the forward direction, the digital display device according to claim 12. The radial focal length of the optical system is reduced in response to the substantial increase of the radial angle at all points of the virtual image from the front direction with a radial angle of more than 20 °, digital display of claim 15 apparatus. The sagittal focal length of the optical system is reduced in response to the substantial increase of the radial angle at all points of the virtual image from the front direction with a radial angle of more than 20 °, digital display of claim 12 apparatus. A headgear comprising the display device according to claim 12 , comprising a mount for positioning the display device on a human head such that an eye position of the display device matches a human eye. 19. The headgear of claim 18 , further comprising a second display device implemented such that an eye position of the second display device matches a second eye of a human. The display device and the second display device are substantially identical, headgear of claim 19. The display of the display and the second display device of the display device is part of a single display, headgear of claim 19.

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